1. Field of the Invention
This invention relates to USB (Universal Serial Bus) devices, and in particular, it relates to a USB device using one USB device controller to simulate multiple virtual USB devices and a virtual USB hub.
2. Description of the Related Art
Conventional USB devices typically use one USB device controller chip for each USB device, and the host computer (e.g. a PC) assigns an address to each USB device. If multiple USB devices are desired, a USB hub is typically required. FIG. 1 shows an example of a USB hub 2 connected to a host computer 1. The USB hub 2 simulates four downstream USB ports, and can control four USB devices. In this example, a USB device 5 (e.g. flash drive, etc.) can be directly plugged to a USB port of the hub 2, or an end user device 4 (e.g. PDA, digital camera, etc.) can be plugged to a USB port of the hub 2 via a cable 3. The cable 3 may be a USB to RS-232 adaptor cable (which is a USB device) with one connector 3a for plugging into an USB port and the other connector 3b for plugging into an RS-232 port of the end user device 4.